1. Field of the Invention
The invention relates to a driving system for a vehicle and, more particularly, to control over a driving system for a vehicle including a continuously variable transmission mechanism and a gear mechanism in parallel with each other.
2. Description of Related Art
There has been suggested a driving system for a vehicle. The driving system includes a continuously variable transmission mechanism, a gear mechanism, and a clutch mechanism between an input shaft and an output shaft. Torque output from a driving force source is transmitted to the input shaft. The output shaft outputs torque to drive wheels. The continuously variable transmission mechanism is able to steplessly change speed ratios. The gear mechanism has at least one gear ratio. The clutch mechanism selectively changes a torque transmission path between a first transmission path and a second transmission path. The first transmission path allows torque to be transmitted via the continuously variable transmission mechanism. The second transmission path allows torque to be transmitted via the gear mechanism. This is, for example, a driving system for a vehicle, described in International Application Publication No. 2013/176208.
International Application Publication No. 2013/176208 describes the driving system for a vehicle, in which a torque transmission path (first transmission path) and a torque transmission path (second transmission path) are provided in parallel with each other. The torque transmission path (first transmission path) includes a continuously variable transmission mechanism that is able to continuously change a speed ratio. The torque transmission path (second transmission path) includes a gear train (gear mechanism) having at least one gear ratio that cannot be set by the continuously variable transmission mechanism. More specifically, the torque transmission path including the gear train is established by connecting a first clutch mechanism and a third clutch mechanism. The first clutch mechanism couples at least two rotating elements selected from among an input element, an output element and a reaction element of a forward/reverse switching mechanism. The forward/reverse switching mechanism is formed of three rotating elements that are able to differentially operate. The third clutch mechanism connects the gear train to an output shaft or disconnects the gear train from the output shaft. Alternatively, the torque transmission path including the continuously variable transmission mechanism is established by connecting a second clutch mechanism. The second clutch mechanism connects a secondary shaft of the continuously variable transmission mechanism to the output shaft or disconnects the secondary shaft from the output shaft. A belt-type continuously variable transmission mechanism is employed as the continuously variable transmission mechanism. The belt-type continuously variable transmission mechanism includes a primary pulley, a secondary pulley and a transmission belt. The primary pulley is coupled to an input shaft. The secondary pulley is coupled to the output shaft. The transmission belt is wound so as to span between the primary pulley and the secondary pulley.